Date of Award


Document Type

Open Access Dissertation


Biological Sciences

First Advisor

James Pinckney


Antibiotics are a cornerstone of modern medicine. Their ability to impair prokaryotic metabolism has saved the lives of many millions of humans in the decades since wide antibiotic usage began. Antibiotic compounds are also widely used in the husbandry of animals that are used for food but, unfortunately, much of the antibiotic mass that goes into humans and animals is excreted unchanged. Those excretions go, directly or indirectly, into aquatic ecosystems. The discovery of this fact has led to a growing global concern about the fate of antibiotics in the environment. This concern is driven by no fewer than three primary facts: 1.) Globally, more than 50% the human population lives within 150 km of major coasts. 2.) Wastewater treatment plants do not specifically remove antibiotics. 3.) Antibiotics tend to bind to particles, which leads to elevated antibiotic levels in the benthos of aquatic systems. These facts have come together to create concern about the antibiotic content of streams, rivers, lakes, and the coastal ocean. The question driving this dissertation is, "Do anthropogenic antibiotics pose a problem for coastal benthic ecosystems?" The work presented here is specifically concerned with the ubiquitous eukaryotic microbial primary producers, the diatoms. Diatoms are found in virtually every type of aquatic system, contributing no less than 40% of the carbon found in many aquatic and aquatically-associated terrestrial species. This dissertation introduces a novel way to rapidly estimate surface-associated diatom cells using in vivo chlorophyll a fluorescence. It further shows that three commonly used, and purportedly prokaryote-only antibiotics can have direct negative effects on some diatom species and that the effects of mixtures of these compounds cannot be predicted a prioi by summing the effects of individual compounds. Finally, I show that the intersection of experimental results from laboratory and those that come from using environmental microbial communities is less than clear. This is done using antibioticimpacted, environmentally-derived microbial communities that were monitored using a combination of traditional physiological measurements and hyperspectral imaging of sediment-surface chlorophyll a.


© 2013, Isaac M. Hagenbuch

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